The number of amplitude modulated broadcast stations that can be accommodated in a $300\, kHz$ bandwidth for the highest modulating frequency of $15\, kHz$ is:

$A$ communications Earth satellite:

The need for modulation is

An antenna is a device:

$A$ carrier wave $v_{c}(t) = 160 \sin(2 \pi \times 10^{6} t) \text{ V}$ is made to vary between $V_{\max} = 200 \text{ V}$ and $V_{\min} = 120 \text{ V}$ by a message signal $v_{m}(t) = A_{m} \sin(2 \pi \times 10^{3} t) \text{ V}$. The peak voltage $A_{m}$ of the modulating signal is ..... .

An antenna uses electromagnetic waves of frequency $5 \text{ MHz}$. For proper working,the size of the antenna should be: